The warning seems to apply to the value of the parameter y -> 1
.
The issue is that the complex-valued principal root does not have -1
in its range. Consider
Arg[x^(1/3)]
(* Arg[x] / 3 *)
It implies that the argument of x^(1/3)
is between ±Pi/3
, since Arg[x]
is between ±Pi
. There are three cube roots of any nonzero complex number, and their arguments differ by 2Pi/3
. There is always exactly one in the sector -Pi/3 < Arg[y] <= Pi/3
. This root is what x^(1/3)
represents.
Therefore the real part of x^(1/3)
is greater than or equal to zero. I believe that Solve[]
is looking at all roots in the complex plane, but there are none.